Aerospace and Electronic Systems Magazine November 2016 Tutorial X - 83

new entrant, it is useful to explore the differences and similarities to
manned aviation that serve as the foundation of the industry today.
In fundamental terms, UAS is more than just an aircraft; it is
a system. It consists of several distinct parts-the flying air vehicle
with the systems onboard (i.e., the unmanned aircraft, or UA), the
ground control station (GCS) that the pilot uses to operate the aircraft, and the command link between the two. By contrast, in almost
all manned aircraft, all of these components are in one place-the aircraft contains the pilot and the control systems, as well as the command links (electrical or mechanical) to the operation of the aircraft.
For the operation of the UAS, the fact that these parts of the
systems are in different places introduces two significant issues.
The first issue surrounds the fact that the human pilot is not on the
aircraft. The UAS pilot does not have first-person awareness of how
the aircraft is performing, or the ability to see out of the aircraft to
understand what is happening in the surrounding environment. The
fundamental advantage that this provides to the pilot of a manned
aircraft is the ability to be able to identify hazardous situations
around the aircraft (other aircraft or obstacles) and immediately direct the aircraft to avoid them. This primary ability to provide "see
and avoid" separation has generated the need for UAS to provide an
SAA capability that is discussed in the bulk of this tutorial.
The second significant issue facing the operation of UAS is the
fact that the human pilot's control of the UA is remote, and typically is dependent on a radio frequency (RF) radio link between
the pilot in the GCS (the equivalent of the cockpit) and the aircraft
itself. There are ways to manage these command and control (C2)
issues-there have been a number of standards development efforts
(through RTCA Special Committee SC-203 and SC-228, as well
as ASTM Committee F38) to define the link reliability requirements, and to have standard methods to ensure that the aircraft will
perform predictably and safely, when the link does fail. The latter
depends on the inclusion of onboard systems for autonomously
controlling the operation of the aircraft, when the pilot is not in
control (by choice or by failure of the link). These autonomous
operations are similar to the manned aircraft autopilot systems, and
must operate in predictable and acceptable ways to be included as
part of the "lost link" solution.
These two main issues (SAA and C2) are the main technical
distinguishers of UAS from manned aircraft operations. Along with
issues of airworthiness and certification standards for UAS, and the
regulatory changes to support UAS as new entrants to the airspace
structures, these represent the roadblocks to the integration of standard UAS operations by aviation authorities around the world.
NOVEMBER 2016, Part II of II

One final, and perhaps most noteworthy point to consider when
analyzing the factors for integrating UAS-the term UAS is used to
cover a wide variety of air vehicles that will be performing a wide
variety of missions, in all kinds of airspace. This means that UAS
are not one thing-it is a general term for a family of devices, for
which there may be different solutions to the core issues of SAA
and C2. Just as manned aircraft range in size from single engine
props to multiengine turbo-jets, UAS can range from larger aircraft
(like Global Hawk and Reaper, that are roughly equivalent in size
to Boeing 737 and Cessna 182, respectively) through midsize aircraft (such as the ScanEagle), to very small sized aircraft (like the
UAS that are growing out of the hobbyist industry). In the United
States, the operation of remotely controlled models for hobbyist
uses (recreational and competition) has been set aside under an
Advisory Circular (FAA AC 91-57). Small commercial UAS may
have had their roots with similar aircraft to the hobbyist (which
have recently become increasingly capable), but the uses have gone
well beyond that of "recreation and entertainment," to commercial
activities and research endeavors. Even for very small aircraft, this
has extended them into areas that require a certified aircraft and
pilot, to operate safely among other aircraft and people.
There have been many efforts to classify UAS by sizes and
operational uses, though none have been accepted as a singular
standard. For this tutorial, we use two main categories to highlight
the major differences in SAA for the large diversity of UAS.
"Large" UAS are aircraft that need to fly among manned
aircraft in controlled airspace. Most countries provide air traffic
control (ATC) services to aircraft flying in this airspace, which include en route high altitude airspace (Class A), terminal airspaces
(Classes B, C, and D), and lower altitude transition airspace (Class
E), as defined by ICAO (see Fig. 1.)

Fig. 1.

Airspace classes.

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